Sedimentology and geochemistry of lacustrine terraces of three Middle Atlas lakes: Holocene paleoclimatic reconstruction in Morocco
Quaternary International, 2012
Abstract In the Moroccan Middle Atlas Mountains, three lakes were used to characterize climate va... more Abstract In the Moroccan Middle Atlas Mountains, three lakes were used to characterize climate variability in the late Holocene. The methodology is based on sedimentological, geochemical, and mineralogical analysis of lacustrine terraces. Lake Ifrah is a natural lake. Waters are calc-magnesian, relatively very alkaline and oxygenated. Lake Afourgagh is of karst origin, with maximum depth 1.5 m. Lake Iffer is a smaller lake, sub-circular and relatively deep. Its area is 3.5 ha. Its maximum depth is 6.5 m at the center of the lake. Seven terraces located in the borders of the lakes were sampled and studied. Seven radiocarbon dates were obtained on organic matter and shells. The time period concerned is between 2300 cal BP and 400 cal BP. The results show high lake levels at about 2300 cal BP related probably to the wetter Iberian – Roman period in northern Mediterranean. Lake Iffer was deeper by about 30 m from its current level. 1000 cal BP probably marks the beginning of the decline with a drop in lake level of 20 m, which is ongoing in connection with drier climate and the beginning of the medieval climate anomaly.
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Papers by DAMNATI BRAHIM
continental areas over the late Quaternary. We have compiled old and new published lake status data from North African
basins, over tree periods: between 30,000 and 21,000 yr B.P, ca 9,000 yr B.P and ca 6,000 yr B.P.
Between 30,000 and 21,000 yr B.P, one or two relatively humid episodes have been identified in northern hemisphere of
Africa. However, at 21,000 yr B.P, Low or intermediate lake status was registered in the Sahara, in west and east Africa
north equator. The scarcity of data in this period globally reflects severe desiccation, deflation and erosion in many basins.
It’s clear that the late glacial maximum was significantly dry in this area.
At 9,000 yr B.P, many lakes began to rise. Some of them receded dramatically after 11,000 yr B.P. The majority of lakes
with this initial amelioration was in north-east Africa in equatorial zone. The large perturbation is occurred in northern
Africa. Between 0° and 22°N, nearly all lakes were high. The water status responded first near the equator (between 0° and
10°N) and subsequently rises progressively in Sahara and Sahel. The main period of positive hydrological conditions was
recorded simultaneously in lacustrine systems in interdunal depression and in Sebkhas in Mauritania, Mali, Eastern Niger
and Sudan.
At 6,000 yr B.P, the lakes show a more positive water balance over northern Africa. The southern margin of the zone of
wetter conditions is unchanged relative to 9,000 yr B.P, but evidence from two sites in the Libyan desert suggests that the
northern boundary may have been slightly further north. There is a suggestion that conditions became wetter than 9,000 yr
B.P (and today) in the Maghreb.
Keywords: Climate, Lakes, data, Africa northern Hemisphere, last glacial maximum, Holocene
regions of the world started several thousand years ago. These interactions have altered rivers to human
dominated systems with often negative impacts on fluvial environments. To achieve a good ecological and
chemical status of rivers, as intended in the European Water Framework Directive (WFD), a better
understanding of the natural status of rivers and an improved quantification of human–riverine interactions
is necessary. Over the last decade the PAGES-LUCIFS (Land Use and Climate Impact on Fluvial Systems)
program has been investigating both contemporary and long-term (centuries tomillennia) river responses to
global change with the principal aims of: 1) quantifying land use and climate change impacts of river-borne
fluxes of water, sediment, C, N and P; 2) identification of key controls on these fluxes at the catchment scale;
and 3) identification of the feedback on both human society and biogeochemical cycles of long-termchanges in
the fluxes of these materials. Here, we review recent progress on identifying fluvial system baselines and
quantifying the response of long-term sediment budgets, biogeochemical fluxes and flood magnitude and
frequency to Holocene global change. Based on this review, we outline the future LUCIFS research agenda
within the scope of the PAGES-PHAROS (Past Human-Climate-Ecological Interactions) research program. Key
research strategies should be focused on: 1) synthesising the data available from existing case studies;
2) targeting research in data-poor regions; 3) integrating sediment, C, N and P fluxes; 4) quantifying the
relative roles of allogenic and autogenic forcing on fluvial regimes, extreme events and sediment fluxes;
5) improving long-term river basin modelling; and 6) integration of LUCIFS with other research communities
within PHAROS, namely HITE (land cover) and LIMPACS (water quality and biodiversity).
have been the main objective of several research studies. These classical methods are very difficult,
time consuming and very expensive. The quantitative estimation of soil loss remains insufficient
particularly in the North of Morocco. In this study, we present results showing the quantification of
the soil erosion using 137Cs and 212Pb in two dam catchments: Raouz and Nakhla.
In the Raouz catchment, the inventories of 137Cs vary between 574 Bq/m2 and 3422 Bq/m2
and of 210Pbexc vary between 274 Bq/m² and 2704 Bq/m². In the second study area situated in the
drainage basin of the Nakhla dam the mean inventories of 137Cs consist between 426 and 777 Bq/m2,
while the mean inventories of 210Pbexc vary between 580 and 891 Bq/m².
The conversion of the inventories in terms of erosion rate and/or accumulation has been done using
a mass balance model (1 and 2) and the 210Pbexc model. The mean erosion rates are respectively
between 8 and 14 t.ha-1.yr-1 and between 18 and 41 t.ha-1.yr-1 using 137Cs models. Using 210Pbexc
model, the mean erosion rate it’s about 20 t.ha-1.yr-1.
These results show the severity of erosion in North West Morocco and the necessity to seek for
urgent and appropriate solutions to stop this problem